Tidal inlet systems are often highly valuable and sometimes even unique ecosystems. However, field measurements show that tidal inlet systems are sensitive to changing exogenous conditions, such as rising sea levels. This thesis aims to investigate to what extent the adjacent sea influences the stability and equilibrium state of the tidal inlet. A one-dimensional idealised model is used to model the interaction between the sea and the inlet. The water motion is forced by the tide and the inlet is assumed to be narrow and short. At equilibrium, an increasingly sloping bottom is found in the sea and a constantly sloping bottom in the inlet. This equilibrium bottom profile seems to be in reasonable agreement with observations. The sea-inlet bottom profile is less stable than the inlet bottom profile, nevertheless, the sea-inlet bottom profile is still asymptotically linear stable. Moreover, the results in this thesis suggest that for one-dimensional idealised models consisting solely of a tidal inlet, the correct seaward boundary condition is a properly chosen fixed entrance depth. For a two-dimensional semi-infinite sea, it is shown that a Perfectly Matched Layer is a convenient method to incorporate the Sommerfeld radiation condition and that the narrow tidal inlet cannot be modelled as a point source forcing in the two-dimensional sea domain.

In this thesis, it is investigated how the blood flow changes in different physiological situations, using a one-dimensional model, that describes the blood flow in compliant vessels. The one-dimensional model, that describes the blood flow, is derived based on the physical laws of conservation of momentum and conservation of mass. A high resolution flux differencing scheme is applied to a stented artery, a tapered artery, an arterial bifurcation and a network of the 55 main arteries in the human arterial tree. It is found that inserting a stent led to an increase in the peak pressure and a dip below the equilibrium pressure, just before the stent. The nonlinearities in the model are shown using a long tapered artery, in the form of the steepening of the pulse. The current treatment of the bifurcations has led to reasonable physical reflections, in the bifurcation test cases. The network of 55 arteries showed that bifurcations play an important role in the blood flow patterns and, as such, they should not be ignored when considering a single blood vessel. Further research should focus on the implementation of a vascular prosthesis and more advanced treatments of the bifurcations.